In the conventional solid polymer electrolyte fuel cell (hereinafter, refer to as “PEFC (Polymer Electrolyte Fuel Cell)”.), an electrical energy generated by an electrochemical reaction produced in a membrane electrode assembly (hereinafter, refer to as “MEA”.) that comprising a plate electrolyte membrane and electrodes (a cathode and an anode) arranged on both sides of the electrolyte membrane is extracted to outside of the PEFC via separators arranged on both sides of the MEA. PEFC can be actuated in a low temperature region. Moreover, because of high energy conversion efficiency, short start-up time, and small-sized and lightweight system, it has attracted attention as a power source of a battery car or a portable power supply.
Meanwhile, a unit cell of the above PEFC comprises such constituent elements as an electrolyte membrane, a cathode and an anode consisting of at least a catalyst layer, and separators, and its theoretical electromotive force is 1.23 volts. However, such a low electromotive force is insufficient as a power source of a battery car or the like. Due to this, a stack PEFC (hereinafter, it may be simply described as “fuel cell”.) configured by arranging end plates or the like on both ends of a stacked body, in which unit cells are stacked in series in the stacking direction, is normally used as a power source. In addition, in order to further improve electric power generation efficiency of the fuel cell, it is preferable to downsize the unit cells and to increase an area of electric-power generating reaction (output density) per unit area.
In order to improve the output density of the conventional plate fuel cell (hereinafter, sometimes refer to as “plate FC”.) per unit area and to improve the electric power generation efficiency thereof, it is necessary to thin the above constituent elements of the plate FC. However, if thickness of the constituent elements of the plate FC is set to be equal to or less than predetermined thickness, functions, strength, and the like of each constituent element may possibly be lowered. For this reason, it is structurally difficult to increase the output density per unit area of the fuel cell having the above-described configuration to be equal to or more than the certain density.
From these view points, in recent years, studies about a tubular-type PEFC (hereinafter, sometimes refer to as “tubular PEFC”.) has been conducted. A unit cell (hereinafter, sometimes refer to as “tubular cell”.) of the tubular PEFC comprises a hollow-shaped MEA (hereinafter, it is simply described as “hollow MEA”.) having a hollow-shaped electrolyte layer and hollow-shaped electrode layers respectively arranged inside and outside of the electrolyte layer. An electrochemical reaction is caused by supplying reaction gases (a hydrogen-based gas and an oxygen-based gas) to the inside and outside of the hollow MEA, and electrical energy generated by the electrochemical reaction is extracted to the outside via current collectors arranged inside and outside of the hollow MEA. Namely, the tubular PEFC facilitates extracting the electrical energy by supplying one of the reaction gas (a hydrogen-based gas or an oxygen-based gas) to the inside of the hollow MEA incorporated in each unit cell and the other reaction gas (an oxygen-based gas or a hydrogen-based gas) to the outside hollow MEA. In other words, since the tubular PEFC allows the outside of two adjacent unit cells to have the same reaction gas, it is possible to omit separators that have gas shielding function in the conventional plate PEFC. Accordingly, the tubular PEFC effectively enables to downsize the unit cell.
Several techniques related to the tubular fuel cell (hereinafter, it may simply refer to as “tubular FC”.) such as tubular PEFC have been disclosed. For example, Published Japanese translations of PCT application No. 2004-505417 discloses an art configured by forming a modular electrochemical cell assembly by bundling a plurality of tubular fuel cells (microcells) and arranging cylindrical heat transfer pipes in the bundle. According to this, the art makes it possible to remove large amount of heat generated by the bundle of microcells.
However, the art disclosed in the Published Japanese translations of PCT application No. 2004-505417, as cooling pipe is in a cylindrical form, one of the tubular fuel cells and one of the cooling pipes contact each other on a line only, it is difficult to improve the cooling efficiency.
Accordingly, an object of the present invention is to provide a fuel cell which is capable to improve heat exchange efficiency with tubular fuel cells.
Disclosure of the Invention
In order to solve the above problems, the present invention takes the following means. The first aspect of the present invention is a fuel cell comprising: a plurality of tubular cells arranged in parallel; and heat exchangers arranged at the outside of the tubular cells, wherein at least a part of the outer circumferential surface of the tubular cells and the peripheral surface of the heat exchangers have face contact with each other.
In the first aspect of the invention, the wording “heat exchangers arranged at the outside of the tubular fuel cell” means that the heat exchangers are arranged so as to have face contact with at least a part of the outer circumferential surface of the tubular cells. In the invention (including the first aspect of the invention and below-described second aspect of the invention), the wording “heat exchanger” means a member having a heat medium passage inside thereof. When a cooling medium runs through the passage, the heat exchanger works as a cooling pipe for cooling the tubular cells. While, when a thermal medium runs through the passage, the heat exchanger works as a heating pipe for heating the tubular cells. Type of heat exchanger of the invention (including the first aspect of the invention and below-described second aspect of the invention) is not limited as long as it has a heat medium passage inside thereof. It is not only a cooling pipe having a single hollow, but also, as described later, it may include a type of heat exchanger in which a plurality of heat medium passages are provided and which is formed by connecting the thick wall portions of the plurality of tubular heat exchangers. Moreover, in the first aspect of the invention, number of the tubular cells to have face contact with a heat exchanger is not particularly limited. A heat exchanger may have face contact with single tubular fuel cell only, or it may have face contact with a plurality (e.g. four or more) of the tubular cells.
The second aspect of the present invention is a fuel cell comprising: a plurality of tubular cells arranged in parallel; and heat exchangers arranged at the outside of the tubular cells, wherein concaves to be directly contact with the outer circumferential surface of the tubular cells are provided onto the peripheral surface of the heat exchangers.
In the second aspect of the invention, the wording “heat exchangers arranged at the outside of the tubular cells” means that the heat exchangers are arranged so as to be in contact with at least a part of the outer circumferential surface of the tubular cells. More specifically, it means that the peripheral surface of one of the heat exchanger and the outer circumferential surface of one of the tubular cells are in line contact with by at least two lines or have face contact with each other. In addition, the wording “concaves to be directly contact with the outer circumferential surface of the tubular cells are provided onto the peripheral surface of the heat exchangers” means that the surface having concaves on which columnar tubular cells can be placed (hereinafter, refer to as “concave”). is provided at the peripheral surface of the heat exchangers. It also means that the concave and the outer circumferential surface of the tubular cells contact each other directly (refer to FIG. 8.). Examples of cross-sectional shape of the concave obtained by cutting in a plane including a direction normal to an axial direction of the heat exchanger include curve profile (refer to FIG. 8(A).), and a polygonal line (refer to FIG. 8(B).). Moreover, in the second aspect of the invention, similar to the first aspect of the invention, number of the tubular cells which have face contact with a heat exchanger is not particularly limited. A heat exchanger may have face contact with single tubular fuel cell only, or it may have face contact with a plurality (e.g. four or more) of the tubular cells.
Further, in the above second aspect of the invention, a cross section of the concaves obtained by cutting in a plane including a direction normal to an axial direction of the heat exchanger may be a polygonal line, and one of the concaves and the outer circumferential surface of one of the tubular cells are in line contact with each other by at least two lines.
In the above second aspect of the invention (including the variation), the outer circumferential surface of the tubular fuel cells and the concave both may be constituted to be curved surface.
Also, in the above second aspect of the invention wherein the outer circumferential surface of the tubular cells and the concaves are constituted to be curved surface, if a curvature radius of the outer circumferential surface of the tubular cells is defined as R1 and a curvature radius of the concave for receiving the tubular cells is defined as R2, a relation R2≦R1 may be given.
In these aspects of the invention (including the first and second aspects, and the variation thereof: hereinafter, same as this), a contact area of the outer circumferential surface of the tubular cells and the peripheral surface of the heat exchanger may be constituted to become 2% or more and 50% or less of the peripheral surface area of the heat exchanger.
In the invention, the wording “contact area is 2% or more and 50% or less of the peripheral surface area of the heat exchanger” means that an area of the peripheral surface of the heat exchanger having face contact with the outer circumferential surface of the tubular cells is 2% or more and 50% or less of the entire peripheral surface area of the heat exchanger. The wording “the entire peripheral surface area” means as follows: in the peripheral surface of a heat exchanger, if an area which contacts with the outer circumferential surface of the tubular cells is defined as “A”; and if another area which does not contact with the outer circumferential surface of the tubular cells is defined as “B”, “the entire peripheral surface area” means the total area shown by “A+B”. In other words, by using A and B, the condition of the above aspects of the invention can be represented by “0.02≦A/(A+B)≦0.5”.
In the aspects of the above invention, reaction gas passages may be formed on the peripheral surface of the heat exchanger to have face contact with the tubular cells.
Further, in the aspects of the above invention, the reaction gas passages may be formed in a direction crossing an axial direction of the tubular cell.
In the aspects of the above invention, the heat exchanger may be disposed in an aperture formed by a plurality of the tubular cells arranged in parallel.
Also, in the aspects of the above invention, a plurality of the heat medium passages may be provided inside the heat exchanger.
In the aspects of the above invention, the peripheral surface of the heat exchanger and the outer circumferential surfaces of four or more of the tubular cells may be arranged to contact each other.
In addition, in the aspects of the above invention, the heat exchanger may have electric conducting property.
In the aspects of the above invention, the heat exchanger may be constituted by an electroconductive material of which outer surface is plated by a precious metal.
Examples of the precious metal include platinum, and gold.
Moreover, in the aspects of the above invention, a cooling medium runs inside of the heat exchanger, at least a part of inner surface to be contacted with the cooling medium may be constituted by an electrical insulating material.
Examples of the cooling medium include water, but also ethylene glycol, and so on.
Furthermore, in the aspects of the above invention, the electrical insulating material may be a silicone rubber.
Effects of the Invention
According to the first aspect of the present invention, since one of the tubular cells and one of the heat exchangers are having face contact with each other, compared with the conventional art that the outer circumferential surface of these tubular cells are in only one line contact with the heat exchanger, it is possible to significantly improve heat exchange efficiency of the tubular cells. Therefore, according to the first aspect of the invention, it is capable to provide a fuel cell which can improve heat exchange efficiency of the tubular cells.
According to the second aspect of the present invention, since one of the tubular cells and one of the heat exchangers are in line contact with each other by at least two lines or have face contact, compared with the conventional art that the outer circumferential surface of these tubular cells are only in line contact with the heat exchanger, it is possible to significantly improve heat exchange efficiency of the tubular cells. Therefore, according to the second aspect of the invention, it is capable to provide a fuel cell which can improve heat exchange efficiency of the tubular cells.
In the second aspect of the invention, since a cross-section of the concaves obtained by cutting in a plane including a direction normal to an axial direction of the heat exchanger is a polygonal line, and one of the concaves and the outer circumferential surface of one of the tubular cells are in line contact with each other by at least two lines, it is capable to improve heat exchange efficiency of the tubular cells.
In the second aspect of the invention, even if the outer circumferential surface of the tubular cells and the concave are curved surface, it is possible for the outer circumferential surface of one of the tubular cells and the peripheral surface (concave) of one of the heat exchangers to be in line contact with each other by at least two lines or to have face contact. Accordingly, by having the constitution, it is capable to improve heat exchange efficiency of the tubular cells.
In the second aspect of the above invention of which concave to be provided with the outer circumferential surface of the tubular cells and with the heat exchanger, as a relation R2≦R1 is given between the curvature radius R1 of the outer circumferential surface of the tubular cells and the curvature radius R2 of the concave, the outer circumferential surface of one of the tubular cells and the peripheral surface (concave portion) of one of the heat exchangers can be in line contact with each other by at least two lines or to have face contact.
In the aspect of the above invention, contact area of the outer circumferential surface of the tubular cells and the peripheral surface of the heat exchanger is set to 2% or more and 50% or less of the peripheral surface area of the heat exchanger. Thereby, it is capable to improve heat exchange efficiency of the tubular cells, and to improve supply efficiency of gases to be supplied to the tubular cells. Accordingly, the aspect of the invention is capable to provide a fuel cell that can improve power generation efficiency.
In addition, in the aspect of the above invention, when the outer circumferential surface of the tubular cells and the peripheral surface of the heat exchangers have face contact with each other because of the reaction gas passages being formed in the peripheral surface of the heat exchangers, it is capable to supply reaction gases to the outer circumferential surface of the tubular cells via these reaction gas passages. Therefore, according to the aspect of the invention, it is possible to provide a fuel cell capable to inhibit the decline in diffusion of reaction gases and to improve heat exchange efficiency of the tubular cells.
Moreover, in the aspect of the above invention, as reaction gas passages are formed in a direction crossing the axial direction of the tubular cells, it becomes possible to diffuse the reaction gases in high flow velocity and to decrease the pressure loss of the reaction gases.
In the aspect of the above invention, by disposing heat exchangers in apertures formed by a plurality of the tubular cells arranged in parallel, it is capable to improve heat exchange efficiency and to downsize the fuel cell.
Further, in the aspect of the above invention, by having a configuration such that a plurality of the reaction gas passages are provided inside the heat exchangers, it is capable to have a configuration formed by connecting the thick wall portion of the heat exchangers to the other heat exchangers. If the heat exchangers have such a configuration, reaction gas passages in the peripheral surface of the heat exchanger can be continuously formed. Thereby, it is possible to easily diffuse reaction gases in high flow velocity and to easily decrease pressure loss of the reaction gases.
In the aspect of the above invention, as the peripheral surface of the heat exchangers and the outer circumferential surface of four or more of the tubular cells are arranged to contact with each other, it is capable to improve heat exchange efficiency and to downsize the fuel cell.
In the aspect of the above invention, as heat exchangers arranged at the outside of the tubular cells have electric conducting property, it is capable to let the heat exchangers to have a function as a current collector. Hence, according to the aspect of the invention, it is capable to provide a fuel cell that can improve current collection efficiency.
In addition, in the aspect of the above invention, since the surface of the heat exchanger to contact with the cooling medium is constituted by the electrical insulating material, together with the above-mentioned effects, it is capable to provide a fuel cell which can inhibit current leakage and improve the electric power generation efficiency.
Furthermore, in the aspect of the above invention of which surface of the heat exchanger which is to contact the cooling medium is constituted by electrical insulating material, by using silicone rubber as an electrical insulating material, it is capable to inhibit current leakage and easily improve electric power generation efficiency.
In the attached drawings, reference numeral 1 indicates a tubular fuel cell, 10a and 10b indicate cooling pipes (heat exchangers), 11 and 12 indicate reaction gas passages, 13 indicates a hole, 15a and 15b indicate apertures, 16 and 17 indicate concaves to be arranged in the heat exchangers, 20 indicates a pipe member, 21a and 21b indicate plate members.